Tempco EN article

[gstopp at fibermux.com]

     Actually the 1k/18.2 ohm divider should be okay current-wise, since 
     the op-amp of the input summer should easily drive a ~1K load into 
     ground. The base of the transistor is not bearing the brunt of this 
     current, as it is merely acting as a sort of buffer here - the current 
     path is to ground.
     
     As for experience with NTC's, I've only used PTC's so somebody else 
     will have to answer that one for you.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Tempco EN article
Author:  The Electro Music Specialist <chaosumb at inch.com> at ccrelayout
Date:    2/4/97 7:06 PM


OK, using the electro.notes. I figured out the mathematics for the Farnell 
NTC (Q81 Tellabs replacement) 1K 3500ppm resistor that many have been 
buying, but putting in place of the Q81 and finding out the temperature 
effect is stronger. Well anyway, in my example, the CV input summer for the 
VCO goes through a voltage divider consisting of a 54.9K 1% and the tempco 
going to ground before reaching the SSM2030's transistor pair base. In 
order to use the NTC resistor, I understand I must use it in the upper leg 
of the divider and the ratio must be constant between the two resistors as 
described in the article. That figures a Rz of 18.2 ohms! Doesn't that seem 
like a steep voltage divider (alot of current) to pass to the base of an 
internal transistor of the SSM2030? 
     
clearing things up:
     
(CV input summer)-->1K -tempco resistor/18.2 ohm voltage
divider to ground--->base of common emmitter pair internal to the SSM2030.
     
How did this work with you people doing this with the ASM1 VCO? I just read 
the article posted about someone doing this thing I'm talking about with 
their ASM1. Hope it works.
     
Stephen